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Post curing response

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tonyrenshaw268(at)gmail.c
Guest

Posted: Wed May 27, 2020 4:34 am Post subject: Post curing response

Thanks Jonathan, Bud, William, and Lance, 

I trialed my setup using my refrigerated van modified camper, cranked it up to 48 degrees Celsius, and now ready to do it properly after considering and making a few changes, like changing my heating source from radiant to ceramic and fan assisted, to minimize any thermal gradient effecting the closest component, even though I am using a fan to swirl around the interior airflow. I do plan on following Guritâ€™s technical data sheet for Ampreg 20,  16 hours at 50 degrees Celsius.

I vaguely recall and would like to ask, can the post cure wait till after wing filling?

I believe not, but have this lingering memory that possibly it could wait. 

Thanks again fellas.

Regards

Tony Renshaw

Sent from my iPad

 	  Quote: 	
		   On 22 May 2020, at 5:02 pm, Europa-List Digest Server <europa-list(at)matronics.com> wrote:

 ï»¿*

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                   Total Messages Posted Thu 05/21/20: 4

         ----------------------------------------------------------

 Today's Message Index:

 ----------------------

   1. 02:52 AM - Post curing question re trailing edges  (Tony Renshaw)

   2. 05:21 AM - Re: Post curing question re trailing edges  (JonathanMilbank)

   3. 04:24 PM - Re: Post curing question re trailing edges  (budyerly(at)msn.com)

   4. 07:09 PM - Re: Post curing question re trailing edges  (William Daniell)

 ________________________________  Message 1  _____________________________________

 Time: 02:52:27 AM PST US

 From: Tony Renshaw <tonyrenshaw268(at)gmail.com>

 Subject: Post curing question re trailing edges

> Gidday,

 I am considering post curing my tailplanes, ailerons and flaps and am wondering

 if people believe I should support the trailing edges, Im very happy with how

 straight they are at the moment, and I dont want to wreck them. I have T shaped

 aluminium straight edges I could use with double sided tape to stabilise them,

 or do people believe with 50 degrees for 15 hours it should be materially

 stable already and should just boil off the hardener? Any advice or suggestions

 about supporting these components would be appreciated, even whether I can simply

 prop them up so air can get completely around them, without any hotspots.

 Im concerned even whether having them rest on specific hard points could be

 an issue at 50 degrees.... personally I think not, but I dont want to find out

 the hard way. 

 Regards

 Tony Renshaw

 ________________________________  Message 2  _____________________________________

 Time: 05:21:11 AM PST US

 Subject: Re: Post curing question re trailing edges

 From: "JonathanMilbank" <jdmilbank(at)yahoo.co.uk>

 Hi again Tony,

 When I did my post curing about 25 years ago, I didn't support the trailing edges

 as far as I can remember. But then I had the leading edges pointing down, so

 the trailing edges were up and unlikely to sag. Also I didn't post cure at 50

 degrees C, rather at 45 to leave a safety margin in case the heat control was

 inaccurate. The end result seemed / is satisfactory.

 To the best of my limited understanding the hardener doesn't "boil off", but simply

 continues to react with the resin while facilitating the hardening process.

 I'm ready to be corrected in this matter. Ampreg 20 is the product which I

 was using.

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=496454#496454

 ________________________________  Message 3  _____________________________________

 Time: 04:24:38 PM PST US

 Subject: Re: Post curing question re trailing edges

 From: "budyerly(at)msn.com" <budyerly(at)msn.com>

 Being in Florida in a hot barn I never have done a heater post cure on the stock

 XS E glass aircraft, during the summer, but on the carbon fiber spar work in

 the winter, I did as the Gurit literature states to do a post cure to achieve

 proper cure of its slower hardeners.

 Never lay a freshly cured aileron flat between supports, it will sag.  Always allow

 a component to cure above 75F-80F for 8-12 hours minimum.  Even Gurit medium

 hardener cures fully at these temperatures.  To get a bit more stiffness one

 should post cure Ampreg 20 series epoxy used in thin components laid up with

 thin glass over foam.  Aeropoxy 2032/PH3660 fully cures at room temp in 8-12

 hours and for those very thin components exposed to desert sun, a heat cure to

 120 F is recommended.  Paint the component any color you want as long as it

 is white and you won't have issues with the glass parts deforming.  Dark colored

 painted surfaces should be heat cured in a  well supported mold or surface

 to preserve their  final shape before heat curing in an oven (normally heated

 to about 140-150F) as the surface temperature will be quite hot for a dark blue

 painted surface, but a white painted surface will be cool to the touch even

 in direct sunlight, therefore high temp heat cure is not necessary for white finished

 Aeropoxy parts.

 In Florida my metal building in the hot sun post cures even Ampreg 20 series within

 one day at roughly 100-110F for 8 hours.  Over a few weeks at these temps

 it really hardens the cure.  For those in a hurry Gurit says 50C or 120F for

 16 hours is sufficient for slow cure hardener (which really stays sticky for a

 long time and does not deep cure without heat ((NASTY).  Dark painted surfaces

 should be cured at a slightly higher temp for about 8 hours.  The Gurit rep

 I contacted was comfortable with a room temp layup and cure of their medium hardener

 if the temps throughout the layup time and cure was accomplished over a

 few days at this warm room temp.  But even if post cured at 50C, the thin glass

 structures like an aileron will not be stiff enough to be stored only supported

 on its ends in a horizontal position if stored in high heat.  He suggested

 that thin parts be stored long axis horizontal with  the parts either vertical

 (TE down or up) if supported only on its ends or just stack it vertical leaning

 against the wall perfectly vertical.

 PTW Aeropoxy preferred all components be supported fully if stored at high temperatures

 (like dessert sun in a hot metal building) even if heat cured to 120

 F.

 Gurit has declared their Ampreg 20 series epoxy laminating systems obsolete.  Their

 new 3X series fully cures at a warm room temp 20C like Aeropoxy 2030. Post

 curing the laminate will greatly increase mechanical/thermal properties. The

 system will achieve similar properties with a cure of 5 hours at 70 - 80C or

 16 hours at 50C. The latter temperature is easily achievable with low cost heating

 and insulation techniques.

 The post cure need not be carried out immediately after laminating. It is possible

 to assemble several composite components and post-cure the

 entire assembly together. It is recommended, however, that elevated temperature

 curing should be completed before any further painting /

 finishing operations. Furthermore, care should be taken to adequately support the

 laminate if it is to be post cured after demoulding, and the

 laminate must be allowed to cool before the support is removed.

 Bottom line:  Properly support your components while curing, post curing, and in

 storage.

 Best Regards,

 Bud Yerly

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=496457#496457

 ________________________________  Message 4  _____________________________________

 Time: 07:09:33 PM PST US

 From: William Daniell <wdaniell.longport(at)gmail.com>

 Subject: Re: Post curing question re trailing edges

 I made supports/cradles from eps

 William Daniell

 LONGPORT

 +57 310 295 0744

>>> On Thu, May 21, 2020, 05:55 Tony Renshaw <tonyrenshaw268(at)gmail.com> wrote:

>>> Gidday,

> I am considering post curing my tailplanes, ailerons and flaps and am

> wondering if people believe I should support the trailing edges, I

 =99m very

> happy with how straight they are at the moment, and I don=99t want

 to wreck

> them. I have T shaped aluminium straight edges I could use with double

> sided tape to stabilise them, or do people believe with 50 degrees for 15

> hours it should be materially stable already and should just boil off the

> hardener? Any advice or suggestions about supporting these components wou

 ld

> be appreciated, even whether I can simply prop them up so air can get

> completely around them, without any hotspots. I=99m concerned even

 whether

> having them rest on specific hard points could be an issue at 50

> degrees.... personally I think not, but I don=99t want to find out

 the hard

> way.

> Regards

> Tony Renshaw

 ===========

 ===========

 ===========

 ===========

 ===========

flyingphil2

Joined: 04 Dec 2009
Posts: 117

Posted: Thu May 28, 2020 7:11 am Post subject: Re: Post curing response

Tony, just out of interest, when were the control surfaces laid up?



I remember having a conversation with Andy Draper about this and I've just read the Gurit 'Guide to Composites'.  As I understand it, post curing is only necessary if you are in a rush and want to crack on with the build.  Otherwise you have to wait but the resin will eventually go off at room temperature and according to the Gurit document that may take 'several hours or even days at room temperature'.  If your control surfaces were built more than a few weeks ago then I believe you can assume the resin is cured if it was mixed correctly.



Have I understood that correctly?  I have some control surfaces in my possession that were laid up in 2001.  They've not been post cured but I'm pretty sure the resin has cured after 19 years!

peterz(at)zutrasoft.com
Guest

Posted: Thu May 28, 2020 7:27 am Post subject: Post curing response

Fwiw, It was my understanding that a post cure raised the Tg (glass transition temp, when it â€˜gets softâ€™ and expands) of the finished product.



Cheers,

Pete



 	  Quote: 	
		   On May 28, 2020, at 11:22 AM, flyingphil2 <philipjtiller(at)gmail.com> wrote:

 

 ï»¿

 

 Tony, just out of interest, when were the control surfaces laid up?

 

 I remember having a conversation with Andy Draper about this and I've just read the Gurit 'Guide to Composites'.  As I understand it, post curing is only necessary if you are in a rush and want to crack on with the build.  Otherwise you have to wait but the resin will eventually go off at room temperature and according to the Gurit document that may take 'several hours or even days at room temperature'.  If your control surfaces were built more than a few weeks ago then I believe you can assume the resin is cured if it was mixed correctly.

 

 Have I understood that correctly?  I have some control surfaces in my possession that were laid up in 2001.  They've not been post cured but I'm pretty sure the resin has cured after 19 years!

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=496545#496545

budyerly@msn.com

Joined: 05 Oct 2019
Posts: 288
Location: Florida USA

Posted: Thu May 28, 2020 1:04 pm Post subject: Post curing response

Yes Pete, 

That is the intension of post cure to â€œstiffenâ€ the glass up to the post cure temp. 

It can in some epoxy/glass increase the tensile strength but little for the compressive strength. 

  

Thanks, 

Bud Yerly 

  

  

Sent from  Mail for Windows 10 

  

  From: owner-europa-list-server(at)matronics.com <owner-europa-list-server(at)matronics.com> on behalf of Pete <peterz(at)zutrasoft.com>

 Sent: Thursday, May 28, 2020 11:24:02 AM

 To: europa-list(at)matronics.com <europa-list(at)matronics.com>

 Subject: Re: Europa-List: Re: Post curing response  

 

  --> Europa-List message posted by: Pete <peterz(at)zutrasoft.com>

 

 Fwiw, It was my understanding that a post cure raised the Tg (glass transition temp, when it â€˜gets softâ€™ and expands) of the finished product.

 

 Cheers,

 Pete

 

 > On May 28, 2020, at 11:22 AM, flyingphil2 <philipjtiller(at)gmail.com> wrote:

 > 

 > ï»¿--> Europa-List message posted by: "flyingphil2" <philipjtiller(at)gmail.com>

 > 

 > Tony, just out of interest, when were the control surfaces laid up?

 > 

 > I remember having a conversation with Andy Draper about this and I've just read the Gurit 'Guide to Composites'.  As I understand it, post curing is only necessary if you are in a rush and want to crack on with the build.  Otherwise you have to wait but the  resin will eventually go off at room temperature and according to the Gurit document that may take 'several hours or even days at room temperature'.  If your control surfaces were built more than a few weeks ago then I believe you can assume the resin is cured  if it was mixed correctly.

 > 

 > Have I understood that correctly?  I have some control surfaces in my possession that were laid up in 2001.  They've not been post cured but I'm pretty sure the resin has cured after 19 years!

 > 

 > 

 > 

 > 

 > Read this topic online here:

 > 

 > http://forums.matronics.com/viewtopic.php?p=496545#496545

 > 

 > 

 > 

 > 

 > 

 > 

 > 

 > 

 >

flyingphil2

Joined: 04 Dec 2009
Posts: 117

Posted: Thu May 28, 2020 1:18 pm Post subject: Re: Post curing response

Ah!

So does it mean that the 'Tg' is essentially room temperature unless you post cure it and raise it to a higher figure?



Does that also mean that unused control surfaces that are 19 years old should still be post cured then?



How many builders did this?  There's no mention of post curing in the build handbook is there?



Thanks,

Phil

peterz(at)zutrasoft.com
Guest

Posted: Thu May 28, 2020 1:49 pm Post subject: Post curing response

No, tg is in the lower hundreds from a room temp cure typically. Post curing typically raises it some 10â€™s of degrees. So itâ€™s not mandatory, but does help somewhat in hot climates.



Best to reference the epoxy spec sheets for specifics.



Cheers,

Pete



 	  Quote: 	
		   On May 28, 2020, at 5:30 PM, flyingphil2 <philipjtiller(at)gmail.com> wrote:

 

 ï»¿

 

 Ah!

 So does it mean that the 'Tg' is essentially room temperature unless you post cure it and raise it to a higher figure?

 

 Does that also mean that unused control surfaces that are 19 years old should still be post cured then?

 

 How many builders did this?  There's no mention of post curing in the build handbook is there?

 

 Thanks,

 Phil

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=496553#496553

budyerly@msn.com

Joined: 05 Oct 2019
Posts: 288
Location: Florida USA

Posted: Thu May 28, 2020 2:18 pm Post subject: Post curing response

Pete, 

One more thing.  Sorry, Iâ€™m out in the field and that answer was too short.   

Ampreg 20 series also has a hard time fully curing fully without heat.  If not brought up to its cure temp it does not come up to its design strength.  So an epoxy cured below its design cure temp will cure very slowly and over time will  cure, but if the component is put into storage or stressed or worse yet put into service before fully cured it will deflect under load more than a glass structure fully cured.     

Iâ€™m afraid I dwell on simple things.  Epoxy should cure at a room temp without the need for heat.  That is why I prefer the epoxy I do and am glad Ampreg has changed their formula. 

Post cure is to stiffen the glass and raise the Tg for sure.  But it is beyond a homebuilders ability to improve the Tg.   However, in testing we found that for those folks in cold climates, the increased post cure of the manufacturers  assured full cure of the epoxy which is more important.  Many believe that the post cure made the epoxy stronger and that it will not â€œliquifyâ€ or loose it structural integrity above the glass transition point.  That is not necessarily true.   

Bruce Neiderer at West Systems did a nice job of explaining how Tg is determined and convinced me that it is more important to get a full cure IAW the manufacturers guidance than curing in cold temps and then post curing at a lower temperature  later on.  There is a time when an epoxy lay up will be fully cured if left at a specific temperature.  This has nothing to do with the Glass Transition Temperature.  Tg is the point where the glass begins to become rubbery.  This is a very high temperature  normally and defines high heat exposure in an aircraft cowl for instance where we must consider protecting the structural epoxy from becoming rubbery.  

As when I talked to Bruce, we normally as builders need to know the following: 

Fully cure the epoxy IAW the manufacturers requirements.   

Donâ€™t worry about the strength from post cure, it is more important to get an assured curing of the epoxy and has nothing to due with overall strength or frankly stiffness.  Itâ€™s all about the cure outâ€¦ 

IF the epoxy / glass structure is exposed to high heat then consider the Tg of the glass, otherwise to a light aircraft or glider builder it is irrelavant... 

Feel free to read his article    https://www.jamestowndistributors.com/userportal/document.do?docId=363 

In his article he explains the Glass Transition Temperature and how it is tested.  Good reading. 

There are also some extensive tests done on high temp vacuum bag cure which is all the rage now as it does two things.  It assures a full cure, no out gassing or bubbles in the cure of the product which reduces strength, and allows the  part to immediately go into service.  Great stuff but beyond our home building capabilities. 

Sorry for the short answer before.  One must always adhere to the epoxy manufacturers recommendations. It is absolutely essential to get a proper cure out of the epoxy, especially if post heating is necessary to assure a proper cure.   If  one cannot meet their cure requirements, use a different epoxy.  Iâ€™m glad all you overseas can use the new Ampreg 3 series and have a more comfortable glass and cure experience without fear of the epoxy not properly curing out. 

Best Regards, 

Bud Yerly 

Sent from  Mail for Windows 10 

From: Pete (peterz(at)zutrasoft.com)

 Sent: Thursday, May 28, 2020 11:32 AM

 To: europa-list(at)matronics.com (europa-list(at)matronics.com)

 Subject: Re: Europa-List: Re: Post curing response 

--> Europa-List message posted by: Pete <peterz(at)zutrasoft.com>

 Fwiw, It was my understanding that a post cure raised the Tg (glass transition temp, when it â€˜gets softâ€™ and expands) of the finished product.

 Cheers,

 Pete

 > On May 28, 2020, at 11:22 AM, flyingphil2 <philipjtiller(at)gmail.com> wrote:

 > 

 > ï»¿--> Europa-List message posted by: "flyingphil2" <philipjtiller(at)gmail.com>

 > 

 > Tony, just out of interest, when were the control surfaces laid up?

 > 

 > I remember having a conversation with Andy Draper about this and I've just read the Gurit 'Guide to Composites'.  As I understand it, post curing is only necessary if you are in a rush and want to crack on with the build.  Otherwise you have to wait but the  resin will eventually go off at room temperature and according to the Gurit document that may take 'several hours or even days at room temperature'.  If your control surfaces were built more than a few weeks ago then I believe you can assume the resin is cured  if it was mixed correctly.

 > 

 > Have I understood that correctly?  I have some control surfaces in my possession that were laid up in 2001.  They've not been post cured but I'm pretty sure the resin has cured after 19 years!

 > 

 > 

 > 

 > 

 > Read this topic online here:

 > 

 > http://forums.matronics.com/viewtopic.php?p=496545#496545

 > 

 > 

 > 

 > 

 > 

 > 

 > 

 > 

 >

rparigoris

Joined: 24 Nov 2009
Posts: 796

Posted: Thu May 28, 2020 5:58 pm Post subject: Re: Post curing response

Hi Group Here's some things Aeropoxy has to say about their Epoxy:

https://www.ptm-w.com/aeropoxy/aeropoxy-faq.html#14

and another:

https://www.ptm-w.com/aeropoxy/AEROPOXY%20Product%20Bulletins/AEROPOXY%20PR2032%20Bulletin%20w-4%20Hardeners%2024Jun08.pdf

Ron P.

Kelvin Weston

Joined: 14 Apr 2010
Posts: 90
Location: Hampshire, UK

Posted: Fri May 29, 2020 6:35 am Post subject: Re: Post curing response

Gents



The Europa Build Manual calls for a post-cure, see Chapter 37, Page 2, which states:



"The first thing that you need to do with your flying surfaces is post-cure them at a temperature between 40 - 50C.  This will improve their strength and cook off any remaining volatiles and moisture within the epoxy system.

Make a simple oven with foam blocks, timber or sheets and an electric fan heater and cure your flying surfaces for 8-10 hours.

Do take care not to get them too hot and make sure that they are fully supported."



The Ampreg 20 and 21 datasheets from Gurit shows an initial cure at a minimum of 18C (ideally 24hrs at 21C) followed by an elevated post-cure of 5 hours at 70 - 80C or 16 hours at 50C.



The datasheet also states:

â€œThe post-cure need not be carried out immediately after laminating. It is possible to assemble several composite components and post-cure the entire assembly together. It is recommended, however, that elevated temperature curing should be completed before any further painting / finishing operations.

Furthermore, care should be taken to adequately support the laminate if it is to be post-cured after demoulding, and the laminate must be allowed to cool before the support is removed.

When post-curing it is recommended to use a ramp rate of 10 degC/hour when heating from ambient to the post-cure temperature, to ensure that the thermal performance of the laminate stays ahead of the oven temperature. Higher ramp rates may result in the resin softening and distortion of the part.â€



The resulting specs with standard hardener for Ampreg 20, 21 and 30 are all very similar and result in a Tg of around:

58C - Room temperature cure (28 days at 21C)

73C - Elevated post cure (16hrs at 50C)



The ultimate Tg for Ampreg 20 and 30 is stated as around 98C.  Ampreg 21 was slightly lower at 91C

_________________
Regards

Kelv Weston
Kit 497
kelv@kdweston.co.uk

m.j.gregory(at)talk21.com
Guest

Posted: Sat May 30, 2020 1:59 am Post subject: Post curing response

A word of caution for those post-curing flying surfaces with blue foam cores: stick to the upper temperature limit of 50C in the Europa Build Manual quoted below. While the Gurit datasheets for Ampreg 20 and 21 also specify elevated post-cure of up to 80C, this may be used for other parts but is too high a temperature for the blue foam. 

 

Some years ago the operator of a commercial oven was being sued because they had heated a Classic wing to 80C for 5 hours instead of the 50C for 8 hours that had been specified by the owner. The result was a wing sagging over the supports, just like the cautionary tale of the Quickie builder mentioned on Page 37-3 of the Manual.

 

Regards,

 

Mike

Dr Mike Gregory

Europa Club Safety Officer

01480 451655

07885 355765

 

--

m.j.gregory(at)talk21.com
Guest

Posted: Sat May 30, 2020 5:04 am Post subject: Post curing response

A word of caution for those post-curing flying surfaces with blue foam cores: stick to the upper temperature limit of 50C in the Europa Build Manual quoted below. While the Gurit datasheets for Ampreg 20 and 21 to



--

flyingphil2

Joined: 04 Dec 2009
Posts: 117

Posted: Mon Jun 01, 2020 1:57 am Post subject: Re: Post curing response

Thanks for all the responses and it looks like I need to post cure the control surfaces then!  



I'm still a little confused.  There are other layups on the Europa - in the wings and in the fuselage (including the u/c layups if you build a tri-gear).  How come these are not required to be post cured?

John Wighton

Joined: 18 May 2010
Posts: 241

Posted: Tue Jun 02, 2020 12:03 am Post subject: Re: Post curing response

Post-curing is essential to achieve optimal bond strength.  This applies to laminated parts and also part to part glued joints.  The regime for the post-curing depends on the system used.  Some systems achieve full strength when exposed to RT (ambient 20 deg C) other require higher temperatures.  Generally higher temperatures result in full post-cure properties being achieved in a shorter time.



Ideally, Europa (composite airframes in general) should be post-cured in their entirety - achieved in an oven with a controlled environment.  A Paintshop facility can provide these conditions.



It should be noted that the Achilles heel of composite aircraft (at least those approved via the LAA) has been the requirement to use a 'Composites Super-Factor' (see LAA TL 1.17).  This takes into account the significant variability in composite strength, stiffness, etc at non-RT conditions.  It also includes a variability factor that accounts for variations in the processes of laminating, jointing, etc.  This CSF can be as high as 1.50.  A reduction in CSF may be negotiated, this is more likely if documented processes and post-cure is followed.   Recent discussions with LAA Engineering indicate that CSF of 1.20 may be possible in some circumstances.  This can have a significant influence on RFs (margins of safety) calculations and even MAUW determination.



My advice to Europa builders is to post-cure their entire airframe.  Survey the airframe to ensure no items are present that will degrade at the chosen post-cure temperature.  



A typical post-cure process will look something like the following (BUT adhere to the supplier instructions and limitations):



1. RT to xxC, ramped up at 1-2C per minute.  

2. Hold (dwell) for 120 mins (typically 80C).

3. Ramp down at 1-2C/min.



The structure should be free (no clamping or holding things down), I would assemble the airframe but this is rarely possible.

_________________
John Wighton
Europa XS trigear G-IPOD

brian.davies44(at)gmail.c
Guest

Posted: Tue Jun 02, 2020 12:29 am Post subject: Post curing response

Hi John,



I recognise your superior knowledge on this subject but is it wise to

recommend that Europa builders in particular post cure their entire

fuselage?  There is now considerable in service experience with Europas that

have not been subject to this treatment and I am not aware of any safety

issues resulting from lack of post cure of the fuselage. I would also apply

the same logic to the XS wings that use factory moulded parts.



Regards



Brian Davies



--

John Wighton

Joined: 18 May 2010
Posts: 241

Posted: Tue Jun 02, 2020 2:35 am Post subject: Re: Post curing response

Brian, thanks for your comment.



I am not aware of any negative influence that a fully cured structure can provide.  



Post-curing of most Europa builds will occur in-service, hot days and heat soak can reach surface temperatures easily exceeding 55C.  Prolonged exposure would compensate for the lack of higher temperatures, eventually.  Hence most Europa will achieve something close to full strength over time.  But that is hardly a controlled process. 



Due to the adoption of generous CSF our Europa aircraft are designed to load levels rarely, if ever, encountered in service.  Crashworthiness aside, the Europa is somewhat over-engineered. 



Given that temperature exposure up to and beyond the Tg is not desireable, as chemical changes occur.  Core temperature range is often cited as a limitation.  However, aircraft materials should have the ability to work from -30C to +80C without degradation.  Otherwise operational limitations will apply.



It's a bit like having a car paint job and driving off before the paint has fully cured.  Why would you?  Sure, the paint will cure eventually, but in the meantime it is soft and will incur scratches and other damages. Maybe an imperfect comparison but hopefully you see what l am talking about.



The tub to lower shell joint, top to bottle shells and wing pin reaction locations all need to achieve full strength. Post-curing to the manufacturer's process instructions is therefore my recommendation.

_________________
John Wighton
Europa XS trigear G-IPOD

kjburns(at)btinternet.com
Guest

Posted: Thu Jun 04, 2020 1:03 am Post subject: Post curing response

Phil ,

All layups are post hardened, either with local temperature controlled heating  (and logger in case of power failure etc.. for a few pounds .. graph can be downloaded on to computer ) ..that is what I did for Tri Gear bracing  ( converted from Mono after 30 hours) ..

You can go the alternative route and build an insulated box for fuselage , and post harden (cure) everything in one go..(control surfaces ,wings , then  fuse depending on stage completion ).



Use peel ply on internal areas like fuel filler cobra to extract excess resin / as post build temperature differences can â€œpullâ€ and deform slightly showing as a slight deformed external skin.



Correct support of components is important, as is keeping within Europa build manual temperatures, ( and resin manufacturers guidelines as there may be differences due to specification changes over the years) ... do not be tempted to bump up the temperature beyond spec .



Statement above is important of you could end up with warping twisting , deamination and damage to cores ..



Manufacturers specifications are the primary references.



Make a mini test oven for your heaters controllers and loggers , make some test components...chocks , cradles , special rigging kit .. and test and tune before doing critical parts.



Post hardening allows lay ups to be worked without clogging tools.

Also when filling control surfaces ..sanding back the filler is less draggy craggy on your favourite abrasives.



These practices are from the hard stuff Slingsby glider repair manual , the UK bible for composite construction and maintenance , cure cycles of 18 to 24 hours are usual ..

Enjoy 



Kevin Burns



Sent from my iPad



[quote] On 2 Jun 2020, at 09:28, Brian Davies <brian.davies44(at)gmail.com> wrote:

 

 

 

 Hi John,

 

 I recognise your superior knowledge on this subject but is it wise to

 recommend that Europa builders in particular post cure their entire

 fuselage?  There is now considerable in service experience with Europas that

 have not been subject to this treatment and I am not aware of any safety

 issues resulting from lack of post cure of the fuselage. I would also apply

 the same logic to the XS wings that use factory moulded parts.

 

 Regards

 

 Brian Davies

 

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